1. Field of the Invention
The present invention relates to a tape cassette provided with spools and a locking member for locking the spools to restrain the spools from unnecessary rotation while the tape cassette is not in use.
2. Description of the Prior Art
There have been various tape cassettes applied to practical uses for the high-density recording of video signals or PCM signals, such as 1/2 in. video tape cassettes and 8 mm video tape cassettes, provided with a locking mechanism for locking the spools to lock the same to prevent the magnetic tape from unwinding while the tape cassettes are not in use.
The locking mechanism locks the spools by pressing a locking member against the spools by the resilience of a spring while the tape cassette is not in use, and unlocks the spools by separating the locking member from the spools with an unlocking pin inserted from outside the case body.
A conventional spool locking mechanism will be described by way of example with reference to FIGS. 18, 19 and 20. Shown in FIGS. 18 to 20 are the case body of a tape cassette 81 consisting of an upper half case 82 and a lower half case 83, holes 84 formed in the upper half case 82 and the lower half case 83, a locking member 91 placed in the lower half case 83, and an unlocking pin 99 that engages the locking member 91 when inserted through the hole 84 in the case body of the tape cassette 81 to shift the locking member 91.
In the following description, a side of the case body of the tape cassette 81 to be placed nearer to a recording/reproducing head will be referred to as "the front side", and a side of the same to be placed farther from the recording/reproducing head will be referred to as "the back side". As best illustrated in FIG. 18 and 19, a substantially rectangular recess 90 is formed in the bottom wall of the lower half case 83 of the case body of the tape cassette 81 in the central portion of the bottom wall and near the back side of the case body of the tape cassette 81, and the locking member 91 is placed in the recess 90 so as to move toward and away from the front side, namely, toward and away from spools 87 and 88.
The locking member 91 has a flat body 91a seated on the bottom surface of the recess 90, and a vertical projection 91b standing upright from the back portion of the flat body 91a. The flat body 91a is provided with a pair of fingers 91a.sub.1 and 91a.sub.2 projected from the opposite ends of the front portion thereof so as to correspond to the spools 87 and 88, respectively.
The spool 87 (88) has an inner spool 87a (88a) which receives a spool driving shaft therethrough, and an outer spool 87b (88b) put on the inner spool 87a (88a) for axial movement relative to the inner spool 87a (88a) and restrained from rotating relative to the inner spool 87a (88a). The fingers 91a.sub.1 and 91a.sub.2 of the locking member 91 can be pressed against portions of the circumferences of the inner spools 87a and 88a projecting from the radial surfaces of the outer spools 87b and 88b, respectively.
A pair of guide slots 92a and 92b are formed in the front portion of the middle portion of the flat body 91a, and guide pins 93a and 93b project from the bottom surface of the recess 90 at positions respectively corresponding to the guide slots 92a and 92b. The guide pins 93a and 93b are received respectively in the guide slots 92a and 92b to guide the locking member 91 for movement in limited directions.
A flat spring 94 for biasing the locking member 91 is disposed behind the locking member 91. The flat spring 94 has a main body 94a, and an arm 94b formed by raising a central portion of the main body 94a. The main body 94a is fitted in a spring pocket 95 formed on the inner surface of the back wall of the lower half case 83, and the extremity of the arm 94b is received in a recess 96 formed in the back surface of the vertical projection 91b to bias the locking member 91 continuously toward the front side of the tape cassette, namely, in a direction to press the fingers 91a.sub.1 and 91a.sub.2 against the circumferences of the inner spools 87a and 88a.
The locking member 91 is provided in the central portion of the front surface of its vertical projection 91b with a triangular protrusion 97 to disengage the locking member 91 from the inner spools 87a and 88a. The triangular protrusion 97 has inclined surfaces 97a and 97b symmetrically descending in opposite directions, respectively, from the apex thereof. An unlocking pin 99 received through the hole 84 of either the upper half case 82 or the lower half case 83 into the case body engages the inclined surface 97a or 97b of the triangular protrusion 97 to unlock the spools 87 and 88 by shifting the locking member 91 toward the back side of the tape cassette.
While the tape cassette 81 is not loaded on a recording/reproducing apparatus, the fingers 91a.sub.1 and 91a.sub.2 are pressed against the circumferences of the inner spools 87a and 88a by the resilience of the flat spring 94 as shown in FIG. 20(a) and as indicated by alternate long and short dash lines in FIG. 19 to lock the spools 87 and 88, so that the spools 87 and 88 are unable to turn even if some shocks act on the tape cassette 81. When the tape cassette 81 is loaded on the recording/reproducing apparatus, the unlocking pin 99 of the recording/reproducing apparatus enters the tape cassette 81 through the hole 84 as shown in FIG. 20(b) and shifts the locking member 91 toward the back side of the tape cassette 81 to a position indicated by continuous lines in FIG. 19 to unlock the spools 87 and 88 by separating the fingers 91a.sub.1 and 91a.sub.2 from the inner spools 87a and 88a.
This conventional locking mechanism has the following problems, which will be described hereinafter with reference to FIGS. 21 to 26.
(1) Since the locking member 91 must be shifted a distance toward the back side of the tape cassette 81 with the unlocking pin 99 received into the tape cassette 81 through the hole 84 of either the upper half case 82 or the lower half case 83 and engaging the triangular protrusion 97 of the locking member 91 to unlock the spools 87 and 88, the holes 84 must be formed outside an area of a width W (FIG. 21) corresponding to the distance by which the locking member 91 must be shifted. Consequently, an area on the surface of the tape cassette available for applying a label 89 is reduced and, if the tape cassette is a very small one, it is impossible to form the label 89 in a size sufficient to indicate all the necessary matters.
(2) The apex of the triangular protrusion 97, i.e., the junction of the inclined surfaces 97a and 97b, in contact with the unlocking pin 99 and expected to move along a course indicated by an alternate long and short dash line is pushed backward away from the course, by the unlocking pin 99, in a region indicated P in FIG. 22, when the back side of the tape cassette 81 is lifted up by the cassette holding mechanism of the recording/reproducing apparatus, in ejecting the tape cassette 81, as shown in FIG. 22, to enable the unlocking pin 99 to escape from the tape cassette 81 through the hole 84 set opposite to the recording/reproducing head of a recording/reproducing apparatus and, consequently, the locking member 91 is moved toward the back side of the tape cassette 81 beyond its normal unlocking position, which produces resistance against the movement of the tape cassette 81 in lifting up the back side of the case body to enable the locking pin 99 to escape from the tape cassette 81, thereby obstructing smooth tape cassette ejection.
(3) The locking member 91 is liable to be tilted by the frictional engagement of the unlocking pin 99 and the triangular protrusion 97 as shown in FIGS. 23(b) or 23(c), increasing the friction between the locking member 91 and the lower half case 83, because it is difficult to form the locking member 91 so that the width L.sub.1 of the flat body 91a is sufficiently large as compared with the height H.sub.1 of the vertical projection 91b, which obstructs smooth spool unlocking operation.
(4) The spools 87 and 88 are biased slightly toward the front side of the tape cassette 81 (in the direction of arrows D.sub.1) by the pressure applied thereto by the locking member 91 in locking the spools 87 and 88 by pressing the locking member 91 against the spools 87 and 88 by the resilience of the flat spring 94 after the unlocking pin 99 has escaped from the tape cassette 81. Consequently, the tape T extending between the spools 87 and 88 is allowed to slacken, nullifying the essential spool locking action of the locking member 91.
(5) It is possible that the spools 87 and 88 are unlocked when the tape cassette 81 is rattled. For example, if external vibrations causing the spools 87 and 88 to turn in the direction of an arrow R.sub.1 as shown in FIG. 25, the spool 87 pushes the locking member 91 in the direction of an arrow D.sub.2 and the spool 88 pushes the locking member 91 in the direction of an arrow D.sub.3, and thereby the spools 87 and 88 are unlocked. Since the spool 88 is urged in the direction of the arrow R.sub.1, the tape T is unwound from the spool 88 and slackens.
The slackening of the tape T due to the rattling of the tape cassette 81 may be obviated by guiding the locking member 91 so that the locking member 91 is translated perfectly. However, when the spools 87 and 88 differ in weight from each other due to the difference between the amount of the tape T wound on the spool 87 and that of the same wound on the spool 88, the lighter one of the spools 87 and 88 is unlocked when the tape cassette 81 is rattled.
(6) The spools 87 and 88 move instantaneously toward the back side, i.e., in the direction of an arrow D.sub.4, as shown in FIG. 26(a) if an impact G is applied to the back side of the tape cassette 81 and, consequently, the spools 87 and 88 are pulled by the tape T and are caused to turn respectively in the directions of arrows R.sub.2 and R.sub.3, and the tape T is unwound from the spools 87 and 88. Accordingly, the tape T slackens by a length pulled out from the spools 87 and 88 when the spools 87 and 88 are moved in the direction of an arrow D.sub.5 to their original positions as shown in FIG. 26(b) by the locking member 91 after the impact G has been removed.
(7) The employment of the flat spring 94 in a locking member biasing means as described with reference to FIGS. 18 and 19 requires the locking member biasing means to be formed in a relatively large construction, which is disadvantageous in application of the locking member biasing means to a very small tape cassette.
Since the arm 94b of the flat spring 94 tending to spring toward the front side of the tape cassette 81 must be strained by the locking member 91 in a direction, namely, toward the back side of the tape cassette 81, opposite the direction in which the arm 94b tends to spring when installing the flat spring 94 in the lower half case 83 or when unlocking the spools 87 and 88, the stress induced in the flat spring 94 increases to cause the flat spring 94 to spring up or to tilt, thereby making the normal spool locking action of the locking member 91 impossible.